An animal's fitness is dependent on its ability to successfully reproduce, a goal that is contingent on the precise coordination of behavior, physiology, and environmental factors. For most animals, energy availability and its biological allocation are the ultimate factors in the regulation of reproduction; the metabolic condition of an animal is therefore tightly linked to its reproductive behavior. One factor recently implicated in the coordination between energy availability and reproduction is the gonadotropin-releasing hormone variant, GnRH II. This peptide is highly conserved across vertebrate species, from fish to humans, and yet little is known about its biological functions. Recent evidence links GnRH II to changes in energy availability as well as feeding and reproductive behaviors. I hypothesize that GnRH II acts as a permissive factor for reproduction based on an animal's nutritional and energetic status. The goal of this proposal is to characterize the relationship between food availability, behavior, and GnRH II, and to determine the peptide's mechanism of action. There are three specific aims: 1.) Determine the receptor subtypes and pathways that GnRH II activates to regulate behavior; 2.) Determine the neural sites of action for GnRH II in the regulation of behavior; 3.) Determine how energetic status affects GnRH II peptide and type-2 GnRH receptor content in the brain. [unreadable] [unreadable]